Reducedness of a ring with prime nilradical Let $A$ be a regular ring and $\mathfrak q$ be an ideal, such that $\sqrt{\mathfrak q}$ is prime. Further assume that $\mathfrak q$ is locally principal (i.e. $\mathfrak q$ is an irreducible divisor which is not necessarily reduced).
Now we assume that $(A/\mathfrak q)_{\sqrt{\mathfrak q}}$ is regular.
Under these hypotheses, we can deduce that $A/\mathfrak q$ is reduced (equivalently $\mathfrak q$ itself is prime) because it is a generically reduced (since $(A/\mathfrak q)_{\sqrt{\mathfrak q}}$ is a zero-dimensional regular local ring, hence a field) Cohen-Macaulay-Ring (since $A$ is regular and $\mathfrak q$ is locally generated by non-zerodivisors).
The geometric interpretation is: If an irreducible component of a divisor $D$ in a regular variety contains a regular point of $D$, then it is a reduced component.
My 2 questions:
1) Can anyone come up with a direct proof (for example not using words like Cohen-Macaulay), which is more elementary?
2) What if we drop the assumption that $\mathfrak q$ is locally principal?
Then the question comes down to:
Let $B$ be a ring (which is a quotient of a regular local Ring) with prime nilradical such that the localization at the nilradical is a field. Does this imply that $B$ is reduced, hence a domain? If not, can someone come up with a counterexample?
All rings can assumed to be Noetherian.
Edit:
Ok, $R=k[x,y]/(x^2,xy)$ should be a counterexample to question 2). We have $nil(R)=(x)/(x^2,xy)$ and $R/nil(R) = k[y]$, so $nil(R)$ is prime. Since we have $xy=0$ in $R$, we deduce $x=0$ in $R_{nil(R)}$, thus the maximal ideal of $R_{nil(R)}$, which is generated by $x$, is zero.
Question 1) is now less interesting because there is no hope to come up with a proof that shows that the "locally principal"-assumption is not necessary at all.
 A: A Noetherian ring is reduced if and only if it is $(R_0)$ and $(S_1)$.  (See, for example, http://stacks.math.columbia.edu/tag/031R )  This condition can be used to provide a simple proof that your ring $A/\mathfrak{p}$ is reduced.
A ring $R$ is $(R_k)$ iff $A_P$ is a regular local ring for all primes $P$ of height at most $k$.  So $R$ is $(R_0)$ iff $R_P$ is regular for all minimal primes $P$.  This is a simple condition and clearly holds for your ring $R = A/{\mathfrak q}$ since it has a unique minimal prime and its localization at that prime is a field.  The assumption that $\mathfrak{q}$ is locally principal is not required here.
A ring $R$ is $(S_k)$ iff $PR_P$ contains a regular sequence in $R_P$ of length at least $\min(k,\mbox{ht} P)$ for every prime $P$ of $R$.  So $R$ is $(S_1)$ iff $PR_P$ contains a nonzerodivisor in $R_P$ for every non-minimal prime $P$ of $R$.  This condition also clearly holds for your ring $R = A/\mathfrak{q}$.  In general the condition required beyond $(R_0)$ is precisely the condition $(S_1)$.
